1. Field of the Invention
The present invention relates to an inner magnet rotor for magnet pumps, and more particularly to an inner magnet rotor for use in magnet pumps which includes magnets of different polarities arranged alternately on a yoke to be drivingly connected to the impeller shaft of the pump.
With such inner magnet rotors for magnet pumps, the magnets on the yoke must be firmly supported at their front and rear ends by holders fixed to the front and rear sides of the yoke. It is required that the holders support the magnets both axially and radially of the rotor.
2. Description of the Prior Art
Conventional inner magnet rotors for magnet pumps fulfilling the above requirement include one having the structure of FIG. 5 (which shows a holder, magnet and yoke only partially). With the prior-art rotor, a stepped portion 102 is formed in the edge of one end of the magnet 101 provided on the yoke 100, i.e. in the magnet shoulder portion, and the holder 103 is formed in its inner side, i.e. in its front side, with a stepped portion 104 complementary to the stepped portion 102. Although FIG. 5 shows the support structure only at one end of each magnet, the other end of the magnet is supported by substantially the same structure as the one shown in FIG. 5.
In the case of the rotor of FIG. 5, the holder 103 is fixed to the yoke 100 with fastening screws 105 schematically represented by a dashed line. The stepped portion 104 of the holder 103 is in engagement with the stepped portion 102 of the magnet 101, holding the magnet 101 axially and radially of the rotor.
The projection 106 of the holder stepped portion 104 of the conventional support structure actually has a small wall thickness radially of the rotor. The small thickness renders the holder 103 unable to support the magnet 101 with sufficient strength with respect to the radial direction. To give the support structure sufficient strength in the radial direction, the projection 106 needs to have a correspondingly increased thickness, which then requires a corresponding decrease in the radius of the stepped portion 102 of the magnet 101. Generally, the magnets for magnet pump inner magnet rotors are prepared from those commercially available and having no stepped portion by machining the magnets to form stepped portions, and are assembled with a yoke and holders into the rotor. The decrease in the radius of the magnet stepped portion 102 presents difficulty in machining, for example, in making the stepped portion 102 fittable to the holder stepped portion 104 with proper accuracy, hence an increased cost.